Network Protocol

All communication, whether face-to-face or over a network, is governed by predetermined rules called protocols. These protocols are specific to the characteristics of the conversation. In our day-to-day personal communication, the rules we use to communicate over one medium, like a telephone call, are not necessarily the same as the protocols for using another medium, such as sending a letter.

Think of how many different rules or protocols govern all the different methods of communication that exist in the world today.

Successful communication between hosts on a network requires the interaction of many different protocols. A group of inter-related protocols that are necessary to perform a communication function is called a protocol suite. These protocols are implemented in software and hardware that is loaded on each host and network device.

One of the best ways to visualize how all of the protocols interact on a particular host is to view it as a stack. A protocol stack shows how the individual protocols within the suite are implemented on the host. The protocols are viewed as a layered hierarchy, with each higher level service depending on the functionality defined by the protocols shown in the lower levels. The lower layers of the stack are concerned with moving data over the network and providing services to the upper layers, which are focused on the content of the message being sent and the user interface.

Using layers to describe face-to-face communication

For example, consider two people communicating face-to-face. As the figure shows, we can use three layers to describe this activity. At the bottom layer, the Physical layer, we have two people, each with a voice that can utter words aloud. At the second layer, the Rules layer, we have an agreement to speak in a common language. At the top layer, the Content layer, we have the words actually spoken-the content of the communication.

Were we to witness this conversation, we would not actually see "layers" floating in space. It is important to understand that the use of layers is a model and, as such, it provides a way to conveniently break a complex task into parts and describe how they work.

At the human level, some communication rules are formal and others are simply understood, or implicit, based on custom and practice. For devices to successfully communicate, a network protocol suite must describe precise requirements and interactions.

Networking protocol suites describe processes such as:

• The format or structure of the message
• The method by which networking devices share information about pathways with other networks
• How and when error and system messages are passed between devices
• The setup and termination of data transfer sessions

Individual protocols in a protocol suite may be vendor-specific and proprietary. Proprietary, in this context, means that one company or vendor controls the definition of the protocol and how it functions. Some proprietary protocols can be used by different organizations with permission from the owner. Others can only be implemented on equipment manufactured by the proprietary vendor.

Often, many of the protocols that comprise a protocol suite reference other widely utilized protocols or industry standards. A standard is a process or protocol that has been endorsed by the networking industry and ratified by a standards organization, such as the Institute of Electrical and Electronics Engineers (IEEE) or the Internet Engineering Task Force (IETF).

The use of standards in developing and implementing protocols ensures that products from different manufacturers can work together for efficient communications. If a protocol is not rigidly observed by a particular manufacturer, their equipment or software may not be able to successfully communicate with products made by other manufacturers.

In data communications, for example, if one end of a conversation is using a protocol to govern one-way communication and the other end is assuming a protocol describing two-way communication, in all probability, no information will be exchanged.

An example of the use of a protocol suite in network communications is the interaction between a web server and a web browser. This interaction uses a number of protocols and standards in the process of exchanging information between them. The different protocols work together to ensure that the messages are received and understood by both parties. Examples of these protocols are:

Application Protocol:

Hypertext Transfer Protocol (HTTP) is a common protocol that governs the way that a web server and a web client interact. HTTP defines the content and formatting of the requests and responses exchanged between the client and server. Both the client and the web server software implement HTTP as part of the application. The HTTP protocol relies on other protocols to govern how the messages are transported between client and server

Transport Protocol:

Transmission Control Protocol (TCP) is the transport protocol that manages the individual conversations between web servers and web clients. TCP divides the HTTP messages into smaller pieces, called segments, to be sent to the destination client. It is also responsible for controlling the size and rate at which messages are exchanged between the server and the client.

Internetwork Protocol:

The most common internetwork protocol is Internet Protocol (IP). IP is responsible for taking the formatted segments from TCP, encapsulating them into packets, assigning the appropriate addresses, and selecting the best path to the destination host.

Network Access Protocols:

Network access protocols describe two primary functions, data link management and the physical transmission of data on the media. Data-link management protocols take the packets from IP and format them to be transmitted over the media. The standards and protocols for the physical media govern how the signals are sent over the media and how they are interpreted by the receiving clients. Transceivers on the network interface cards implement the appropriate standards for the media that is being used.

address range of each IPv4 network

Within the address range of each IPv4 network, we have three types of addresses:

Network address - The address by which we refer to the network

Broadcast address - A special address used to send data to all hosts in the network

Host addresses - The addresses assigned to the end devices in the network

Network Address

The network address is a standard way to refer to a network. For example, we could refer to the network shown in the figure as "the 10.0.0.0 network." This is a much more convenient and descriptive way to refer to the network than using a term like "the first network." All hosts in the 10.0.0.0 network will have the same network bits.

Within the IPv4 address range of a network, the lowest address is reserved for the network address. This address has a 0 for each host bit in the host portion of the address.

Roll over the NETWORK ADDRESS tab in the figure.

Broadcast Address

The IPv4 broadcast address is a special address for each network that allows communication to all the hosts in that network. To send data to all hosts in a network, a host can send a single packet that is addressed to the broadcast address of the network.

The broadcast address uses the highest address in the network range. This is the address in which the bits in the host portion are all 1s. For the network 10.0.0.0 with 24 network bits, the broadcast address would be 10.0.0.255. This address is also referred to as the directed broadcast.

Roll over the BROADCAST ADDRESS tab in the figure.

Host Addresses

As described previously, every end device requires a unique address to deliver a packet to that host. In IPv4 addresses, we assign the values between the network address and the broadcast address to the devices in that network.

Addresing network in IPv4

Each device on a network must be uniquely defined. At the Network layer, the packets of the communication need to be identified with the source and destination addresses of the two end systems. With IPv4, this means that each packet has a 32-bit source address and a 32-bit destination address in the Layer 3 header.

These addresses are used in the data network as binary patterns. Inside the devices, digital logic is applied for their interpretation. For us in the human network, a string of 32 bits is difficult to interpret and even more difficult to remember. Therefore, we represent IPv4 addresses using dotted decimal format.

Dotted Decimal

Binary patterns representing IPv4 addresses are expressed as dotted decimals by separating each byte of the binary pattern, called an octet, with a dot. It is called an octet because each decimal number represents one byte or 8 bits.

For example, the address:

10101100000100000000010000010100

is expressed in dotted decimal as:

172.16.4.20

Keep in mind that devices use binary logic. The dotted decimal format is used to make it easier for people to use and remember addresses.

Network and Host Portions

For each IPv4 address, some portion of the high-order bits represents the network address. At Layer 3, we define a network as a group of hosts that have identical bit patterns in the network address portion of their addresses.

Although all 32 bits define the IPv4 host address, we have a variable number of bits that are called the host portion of the address. The number of bits used in this host portion determines the number of hosts that we can have within the network.

Click the labels in the figure to see the different parts of the address.

For example, if we need to have at least 200 hosts in a particular network, we would need to use enough bits in the host portion to be able to represent at least 200 different bit patterns.

To assign a unique address to 200 hosts, we would use the entire last octet. With 8 bits, a total of 256 different bit patterns can be achieved. This would mean that the bits for the upper three octets would represent the network portion.

Note: Calculating the number of hosts and determining which portion of the 32 bits refers to the network will be covered later in this chapter.

To understand the operation of a device in a network, we need to look at addresses and other data the way the device does - in binary notation. This means that we need to have some skill in binary to decimal conversion.

Data represented in binary may represent many different forms of data to the human network. In this discussion, we refer to binary as it relates to IPv4 addressing. This means that we look at each byte (octet) as a decimal number in the range of 0 to 255.

Positional Notation

Learning to convert binary to decimal requires an understanding of the mathematical basis of a numbering system called positional notation. Positional notation means that a digit represents different values depending on the position it occupies. More specifically, the value that a digit represents is that value multiplied by the power of the base, or radix, represented by the position the digit occupies. Some examples will help to clarify how this system works.

For the decimal number 245, the value that the 2 represents is 2*10^2 (2 times 10 to the power of 2). The 2 is in what we commonly refer to as the "100s" position. Positional notation refers to this position as the base^2 position because the base, or radix, is 10 and the power is 2.

Using positional notation in the base 10 number system, 245 represents:

245 = (2 * 10^2) + (4 * 10^1) + (5 * 10^0)

or

245 = (2 * 100) + (4 * 10) + (5 * 1)

Binary Numbering System

In the binary numbering system, the radix is 2. Therefore, each position represents increasing powers of 2. In 8-bit binary numbers, the positions represent these quantities:

2^7 2^6 2^5 2^4 2^32^2 2^1 2^0

128 64 32 16 8 4 2 1

The base 2 numbering system only has two digits: 0 and 1.

When we interpret a byte as a decimal number, we have the quantity that position represents if the digit is a 1 and we do not have that quantity if the digit is a 0, as shown in the figure.

1 1 1 1 1 1 1 1

128 64 32 16 8 4 2 1

A 1 in each position means that we add the value for that position to the total. This is the addition when there is a 1 in each position of an octet. The total is 255.

128 + 64 + 32 + 16 + 8 + 4 + 2 + 1 = 255

A 0 in each position indicates that the value for that position is not added to the total. A 0 in every position yields a total of 0.

0 0 0 0 0 0 0 0

128 64 32 16 8 4 2 1
0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 = 0

Notice in the figure that a different combination of ones and zeros will yield a different decimal value.

See the figure for the steps to convert a binary address to a decimal address.

In the example, the binary number:

10101100000100000000010000010100

Is converted to:

172.16.4.20

Keep these steps in mind:

Divide the 32 bits into 4 octets.
Convert each octet to decimal.
Add a "dot" between each decimal.

Not only do we need to be able to convert binary to decimal, we also need to be able to convert decimal to binary. We often need to examine an individual octet of an address that is given in dotted decimal notation. Such is the case when the network bits and host bits divide an octet.

As an example, if a host with the 172.16.4.20 were using 28 bits for the network address, we would need to examine the binary in the last octet to discover that this host is on the network 172.16.4.16. This process of extracting the network address from a host address will be explained later.

Address Values are Between 0 and 255

Because our representation of addresses is limited to decimal values for a single octet, we will only examine the process of converting 8-bit binary to the decimal values of 0 to 255.

To begin the conversion process, we start by determining if the decimal number is equal to or greater than our largest decimal value represented by the most-significant bit. In the highest position, we determine if the value is equal to or greater than 128. If the value is smaller than 128, we place a 0 in the 128-bit position and move to the 64-bit position.

If the value in the 128-bit position is larger than or equal to 128, we place a 1 in the 128 position and subtract 128 from the number being converted. We then compare the remainder of this operation to the next smaller value, 64. We continue this process for all the remaining bit positions.

See the figure for an example of these steps. We convert 172 to 10101100.

LAN Local Area Network

Networks infrastructures can vary greatly in terms of:

1. The size of the area covered
2. The number of users connected
3. The number and types of services available

An individual network usually spans a single geographical area, providing services and applications to people within a common organizational structure, such as a single business, campus or region. This type of network is called a Local Area Network (LAN). A LAN is usually administered by a single organization. The administrative control that governs the security and access control policies are enforced on the network level.

When a company or organization has locations that are separated by large geographical distances, it may be necessary to use a telecommunications service provider (TSP) to interconnect the LANs at the different locations. Telecommunications service providers operate large regional networks that can span long distances. Traditionally, TSPs transported voice and data communications on separate networks. Increasingly, these providers are offering converged information network services to their subscribers.

Individual organizations usually lease connections through a telecommunications service provider network. These networks that connect LANs in geographically separated locations are referred to as Wide Area Networks (WANs). Although the organization maintains all of the policies and administration of the LANs at both ends of the connection, the policies within the communications service provider network are controlled by the TSP.

WANs use specifically designed network devices to make the interconnections between LANs. Because of the importance of these devices to the network, configuring, installing and maintaining these devices are skills that are integral to the function of an organization's network.

LANs and WANs are very useful to individual organizations. They connect the users within the organization. They allow many forms of communication including exchange e-mails, corporate training, and other resource sharing.
Although there are benefits to using a LAN or WAN, most of us need to communicate with a resource on another network, outside of our local organization.

Examples of this type of communication include:
Sending an e-mail to a friend in another country
Accessing news or products on a website
Getting a file from a neighbor's computer
Instant messaging with a relative in another city
Following a favorite sporting team's performance on a cell phone

Internetwork

A global mesh of interconnected networks (internetworks) meets these human communication needs. Some of these interconnected networks are owned by large public and private organizations, such as government agencies or industrial enterprises, and are reserved for their exclusive use. The most well-known and widely used publicly-accessible internetwork is the Internet.

The Internet is created by the interconnection of networks belonging to Internet Service Providers (ISPs). These ISP networks connect to each other to provide access for millions of users all over the world. Ensuring effective communication across this diverse infrastructure requires the application of consistent and commonly recognized technologies and protocols as well as the cooperation of many network administration agencies.

Intranet

The term intranet is often used to refer to a private connection of LANs and WANs that belongs to an organization, and is designed to be accessible only by the organization's members, employees, or others with authorization.

Note: The following terms may be interchangeable: internetwork, data network, and network. A connection of two or more data networks forms an internetwork - a network of networks. It is also common to refer to an internetwork as a data network - or simply as a network - when considering communications at a high level. The usage of terms depends on the context at the time and terms may often be interchanged.
 Important terms to remember are:

Network Interface Card - A NIC, or LAN adapter, provides the physical connection to the network at the PC or other host device. The media connecting the PC to the networking device plugs directly into the NIC.

Physical Port - A connector or outlet on a networking device where the media is connected to a host or other networking device.

Interface - Specialized ports on an internetworking device that connect to individual networks. Because routers are used to interconnect networks, the ports on a router are referred to network interfaces.

Networks fundamental

We now stand at a critical turning point in the use of technology to extend and empower our human network. The globalization of the Internet has succeeded faster than anyone could have imagined. The manner in which social, commercial, political and personal interactions occur is rapidly changing to keep up with the evolution of this global network. In the next stage of our development, innovators will use the Internet as a starting point for their efforts - creating new products and services specifically designed to take advantage of the network capabilities. As developers push the limits of what is possible, the capabilities of the interconnected networks that form the Internet will play an increasing role in the success of these projects.

This chapter introduces the platform of data networks upon which our social and business relationships increasingly depend. The material lays the groundwork for exploring the services, technologies, and issues encountered by network professionals as they design, build, and maintain the modern network.

In this chapter, you will learn to:

• Describe how networks impact our daily lives.
• Describe the role of data networking in the human network.
• Identify the key components of any data network.
• Identify the opportunities and challenges posed by converged networks.
• Describe the characteristics of network architectures: fault tolerance, scalability, quality of service and security.
• Install and use IRC clients and a Wiki server.

Among all of the essentials for human existence, the need to interact with others ranks just below our need to sustain life. Communication is almost as important to us as our reliance on air, water, food, and shelter.

The methods that we use to share ideas and information are constantly changing and evolving. Whereas the human network was once limited to face-to-face conversations, media breakthroughs continue to extend the reach of our communications. From the printing press to television, each new development has improved and enhanced our communication.

As with every advance in communication technology, the creation and interconnection of robust data networks is having a profound effect.

Early data networks were limited to exchanging character-based information between connected computer systems. Current networks have evolved to carry voice, video streams, text, and graphics between many different types of devices. Previously separate and distinct communication forms have converged onto a common platform. This platform provides access to a wide range of alternative and new communication methods that enable people to interact directly with each other almost instantaneously.

The immediate nature of communications over the Internet encourages the formation of global communities. These communities foster social interaction that is independent of location or time zone.